1. Field of the Invention
The present invention relates to a synthetic polymer multifilament yarn and a process for producing the same. More particularly, the present invention relates to a synthetic polymer multifilament yarn capable of being converted to a bulky yarn and of being evenly dyed, and useful for woven or knitted fabrics having a silky gloss and draping property, and a process for producing the same.
2. Description of the Related Arts
It is known from, for example, U.S. Pat. No. 3,200,576, that a synthetic polymer multifilament yarn capable of being converted to a bulky yarn by applying heat thereto is prepared by mixing two types of filaments having a different thermal shrinkage. When this type of multifilament yarn is heat-treated a large shrinkage of the high shrinkage filaments in the yarn occurs, causing the low shrinkage filaments in the yarn to overhang from the yarn and thus make the yarn bulky.
Where the high shrinkage filaments have a large thickness and the low shrinkage filaments have a small thickness, the resultant heat-treated multifilament bulky yarn exhibits a high modulus and a soft touch.
U.S. Pat. No. 4,153,660 discloses a process for producing a multifilament yarn capable of being converted to a bulky yarn by a heat treatment in a manner such that a polymer melt is extruded through a number of spinning orifices, a number of the resultant polymer melt filamently streams are rapidly cooled, the resultant undrawn filaments are divided into two bundles, each consisting of a plurality of individual filaments, an aqueous spinning-finishing agent is applied to a filament bundle, and a finishing agent having a higher boiling temperature than that of water is applied to the other filament bundle. The two bundles are then separately drawn under the same conditions while being heat-treated, and the drawn bundles are incorporated with each other to mix the two types of filaments having a different heat shrinkage.
The above-mentioned process imparts different thermal shrinkage to the two separate filament bundles due to the difference in boiling temperature between the two different finishing agents. However, the separate applications of the two different finishing agent make the process very complicated.
Where two separate types of filament having different deniers are produced from the same type of filaments extruded through the same spinneret, undesirable adhesion or breakage of the filaments often occurs due to lateral movement of the filaments extruded through the spinneret. To prevent this, the spinning process conditions, including a draft for the filaments and a flow rate of cooling air, must be strictly controlled.
U.S. Pat. Nos. 4,332,757 and 4,349,604 disclose a process for producing a multifilament yarn capable of being converted to a bulky yarn, which process does not entail the above-mentioned complicated operations.
In this process, a polymer melt is extruded through two separate spinning openings having different opening diameters and facing each other at a predetermined angle, the extruded two separate filamentary streams of the polymer melt are brought into contact with each other immediately below the spinneret, while one filamentary stream is made to travel in a sinuous manner, the resultant composite filamentary stream of the polymer melt is rapidly cooled, and the resultant solid filament is taken up.
The resultant individual filament, which is referred to as a pulsing filament, has a shrinkage varying not only in the longitudinal direction but also in the lateral direction thereof.
Usually, the multifilament yarn is converted to a woven or knitted fabric and then a heat treatment is applied to the fabric to convert the multifilament yarn to a bulky yarn, and accordingly, the fabric to a bulky fabric.
However, the bulky fabric produced from the pulsing multifilament yarn usually exhibits an unsatisfactory bulkiness. This is because, due to the restriction effect of the weaving or knitting structure of the fabric to shrinkage of the multifilament yarn therein, the shrinking force of the pulsing filament yarn is not sufficiently large, and therefore, the shrinkage of the pulsing filament yarn is restricted.
Also, the pulsing filament yarn has an disadvantage in that, when a drawing operation and heat-setting operation are applied to the yarn to impart the enhanced mechanical properties necessary for practical use to the yarn, the local difference in shrinkage retained in the pulsing filaments is lost, and accordingly, the pulsing multifilament yarn must be utilized to produce a bulky yarn or fabric without applying the drawing and heat-setting procedures thereto. Therefore, the bulky yarn or fabric produced from the pulsing multifilament yarn sometimes exhibits an uneven shrinkage and a local plastic deformation of the individual filaments when a stress is applied to the yarn or fabric.
U.S. Pat. Nos. 4,546,043 and 4,631,162 disclose a synthetic polymer multifilament yarn capable of being uniformly converted to a bulky yarn having a high bulkiness without generating an undesirably uneven shrinkage and plastic deformation. In this type of multifilament yarn, each individual filament is composed of a hollow filamentary constituent, a non-hollow, sinuous filamentary constituent in a wave form having a smaller thickness than that of the hollow filamentary constituent, and a middle filamentary constituent through which the hollow filamentary constituent is connected to the non-hollow filamentary constituent. This type of multifilament yarn is produced by extruding a synthetic polymer melt through a plurality of spinning orifices each consisting of a hollow filament-forming orifice segment, a non-hollow filament-forming orifice segment having a size smaller than that of the hollow filament-forming orifice segment, and a thin slit-formed orifice segment through which the hollow filament-forming orifice segment is connected to the non-hollow filament-forming orifice segment. A portion of the polymer melt is extruded through the non-hollow filament-forming orifice segment at a larger extruding rate than that of the portion extruded through the hollow filament-forming orifice segment, and the resultant non-hollow filamentary stream of the polymer melt travels in a sinuous manner, while being connected to a hollow filamentary stream of the polymer melt extruded through the hollow filament-forming orifice segment, through a filamentary stream of the polymer melt extruded through the thin slit-formed orifice segment. The resultant connected filamentary streams are solidified by cooling and taken up.
In this type of the multifilament yarn, each individual filament has a large difference in shrinkage between the hollow filament constituent and the non-hollow filament constituent thereof, and thus can be converted to a high bulky yarn even after the multifilament yarn is drawn.
However, when the above-mentioned type of multifilament bulky yarn is converted to a woven or knitted fabric, the resultant fabric sometimes exhibits an uneven dyeing property, and therefore, the above-mentioned multifilament yarn is not useful for high quality woven or knitted fabrics required to have a silky gloss and draping property and to exhibit a beautiful and elegant appearance and touch.
Recently, the high quality woven or knitted fabrics are further required to exhibit an enhanced wearing comfort, and thus to have a high antistatic property and an improved moisture-absorbing property. Accordingly, new types of synthetic polymer multifilament yarns having the above-mentioned enhanced properties are in demand when making more comfortable cloth.
The inventors of the present invention found that the shrinkage of the multifilament yarn disclosed in U.S. Pat. Nos. 4,546,043 and 4,631,162 is too uneven, due to the unevenness in the thickness of the individual filaments in the longitudinal direction thereof, and therefore, the woven or knitted fabrics composed of the multifilament yarn are dyed unevenly.
The unevenness in the shrinkage of each individual filament along the longitudinal axis of the filament can be eliminated by controlling the variance in the thickness of the filament along the longitudinal axis of the filament, and by controlling the difference in the extruding rate of the hollow filamentary constituent stream and the non-hollow filamentary stream of the polymer melt.
However, if the difference in the extruding rate is controlled to a too small level, the variance in the thickness in the filament becomes too small, and although this too small variance in the thickness results in a too small bulkiness of the resultant yarn or fabric, it is effective for removing the unevenness in dyeing of the resultant yarn or fabric. Also, it was found that, when the hollow filamentary stream of the polymer melt extruded at a low extruding rate is brought into contact with the non-hollow filamentary stream of the polymer melt extruded at a high extruding rate, the resultant individual filament has a large unevenness in thickness of the filament along the longitudinal axis of the filament.
In view of the above-mentioned, it was assumed by the inventors of the present invention that, if the thickness of the high extruding rate filamentary stream of the polymer melt could be varied in a pulsing condition without coming into direct contact with the low extruding rate filamentary stream, the aforementioned objects of the present invention could be attained.
In an attempt made on the basis of that assumption, a polymer melt was extruded through a complicated spinning opening composed of at least two I-shaped opening segments facing the core opening segment arranged between the I-shaped opening segments and at least two thin slit-shaped opening segments, in such a manner that a portion of the polymer melt was extruded through the I-shaped opening segments at a smaller extruding rate than that of another position of the polymer melt extruded through the core opening segment. It was found that a sinuous filamentary stream of the polymer melt extruded through the core opening segment was formed while varying the thickness thereof in pulsing form, and was connected to two belt-shaped filamentary streams of the polymer melt extruded through the I-shaped opening segment through two filamentary streams of the polymer melt extruded through the thin slit-formed opening segments. Further, it was found that the resultant irregular multifilament yarn was useful for producing a bulky woven or knitted fabric having a high bulkiness and a uniform dyeing property.